The present invention relates to a recording apparatus capable of recording on recording paper with a paper width of almost size A1 or B1 at the maximum and, more particularly, relates to a recording apparatus including a transport roller structure which is suitable for ensuring the stable transport of the paper at a center supporting portion which supports a long transport roller for transporting the recording paper at the center portion thereof to thereby suppress the occurrence of cockling phenomenon.
Most of large-sized recording apparatuses employ such a structure that a paper feeding section is disposed at the upper portion in the rear of the main body of the recording apparatus, recording paper is fed toward the front portion of the recording apparatus from the paper feeding section and transported to a recording section by way of a slanted paper transport path, then the paper subjected to the recording process is ejected in the slanted downward direction from a paper ejecting section, and the paper thus ejected is received by a receiving unit provided at the lower portion of the recording apparatus.
In such a recording method, the recording paper in the form of a paper in which paper is wound on a core, or a cut sheet is fed to the recording section and the recording is conducted by a recording head which is mounted on a carriage and moves reciprocally.
A paper feeding section is constituted by a transport roller driven and rotated by a motor and a driven roller which rotates in accordance with the rotation of the transport roller. The paper feeding section is disposed near the recording head and arranged in a manner that the driven roller acts to press the recording paper against the transport roller thereby to transport the recording paper toward the recording area where the recording head exists.
A large-sized recording apparatus accorded to the wide recording paper requires a long transport roller corresponding to the width of the recording paper, so that a paper feeding section thereof employs the structure that many driven rollers are disposed in parallel to the long transport roller. In this respect, in order to feed the recording paper with a high accuracy, a spring member is provided at every driven roller so that a predetermined urging force is uniformly applied to the entire width of the recording paper to thereby push the recording paper against the transport roller.
Such a long transport roller bends at the center portion thereof due to various reasons. At the time of the fabrication, the transport rollers bend slightly due to mechanical allowance or tolerance. Further, when the transport roller is laid so as to be supported at the both ends thereof, the transport roller bends at its center portion due to its own weight. Furthermore, the degree of the flexure of the transport roller differs depending on that the roller is formed as a tubular member or a pillar member. For example, when the roller is formed by a thin-walled tubular member, the roller has such a nature that the thicker the wall thickness becomes, the less the roller bends.
Such a bending phenomenon of the transport roller degrades the transporting accuracy of the recording paper and results in the degradation of the recording quality thereof. As a countermeasure for such a phenomenon, when the diameter of the transport roller is made large to such a degree for preventing the bending of the roller caused by its own weight, there arises such a problem that a larger space for disposing such a transport roller is required and the size of a bearing portion also becomes large. Accordingly, such a transport roller with a large diameter is not practical.
Further, since the transport roller is applied with pressure (load) from the driven rollers, the transport roller also bends due to this pressure. When comparing the bending amount of the transport roller due to the mechanical allowance, tolerance upon fabricating the rollers, or its own weight with the bending amount due to the load of the driven rollers, the latter amount is larger than the former amount. In particular, a bending amount becomes larger due to the multiplier effect of these bending phenomena, and this bending amount becomes larger as the length of the transport roller becomes longer and the diameter of the transport roller becomes smaller, so that the transporting accuracy of the recording paper is further influenced.
As a countermeasure for such influence, it is considered to provide such a structure that the transport roller is supported at the center portion thereof to thereby suppress the bending phenomenon of the transport roller. According to this center supporting structure for supporting the transport roller, since a slight concave is formed at the portion where the transport roller is supported, there arises such a problem that, due to the presence of the concave portion, the transporting operation of the paper becomes unstable and the concave portion likely becomes an origin for generating the cockling phenomenon that the recording paper is moisten by ink and so expands and waves.
Accordingly, an object of the invention is to provide a recording apparatus which can suppress the unstable transporting operation of papers at the center supporting portion of a transport roller and also suppress the generation of origin of cockling phenomenon.
In order to achieve the above object, according to the present invention, there is provided a recording apparatus comprising:
a first roller arranged parallel with a main direction of a recording head for transporting a recording paper, the paper transporting roller including a first portion provided with a surface having a first friction coefficient and a first diameter, and a second portion provided with a surface having a second friction coefficient larger than the first friction coefficient and a second diameter larger than the first diameter;
a second roller driven by the first roller while providing pressure to be applied onto the recording paper toward the first roller, the second roller opposed to the first roller such that a roller surface thereof extends over a boundary of the first portion and the second portion of the first roller; and
a supporting member for supporting the first portion of the first roller rotatably thereon.
In this configuration, since the paper is transported while being gripped by the second roller (driven roller) and the second portion (high-friction surface) of the first roller (paper transport roller), high paper transporting accuracy can be attained and so the degradation of recording quality can be prevented. Further, when the driven roller provides pressure against the transport roller, the surface of the driven roller is slightly so deformed elastically as to be bent toward the first portion (low-friction surface) to thereby press the recording paper against the low-friction surface of the transport roller.
Thus, a force for gripping the paper surely acts on the paper and so the paper can be transported stably even though the transport roller is provided with the low-friction surface which diameter is slightly smaller than that of the high-friction surface. Further, the recording paper running between the driven roller and the low-friction surface of the transport roller is restricted in its position by the surface of the driven roller in a state that the surface of the driven roller extends over the low-friction surface and the high-friction surface at the boundary portions between the low-friction surface and the high-friction surface and the elastically-deformed driven roller almost eliminates the gap with respect to the low-friction surface, so that the generation of origin of the cockling phenomenon at the low-friction surface portion can be suppressed.
Preferably, the supporting member is arranged so as to oppose to the second roller through the first roller.
In this configuration, when the load of the driven roller is applied to the transport roller, the load is received by the supporting member through the transport roller, it is possible to suppress the bending of the transport roller.
Preferably, the roller surface of the second roller extends so as to oppose to an entire width of the first portion of the first roller.
In this configuration, since the surface of the driven roller is disposed in opposite to the entire width of the low-friction surface of the transport roller, the transporting stability of the recording paper which is transported while opposing to the low-friction surface can be further improved. Further, the generation of origin of the cockling phenomenon can be suppressed not only at the low-friction surface portion but over the entire width of the low-friction surface.
Alternatively, the roller surface of the second roller extends so as to oppose to a part of the first portion of the first roller.
In this configuration, since a driven roller to be positioned in opposition near the center portion of the low-friction surface, at which origin of the cockling phenomenon is hardly generated, can be eliminated, a more economical supporting member can be provided.
Preferably, the roller surface of the second roller opposes to both widthwise end portion of the first portion of the first roller.
In this configuration, since a uniform pressure is applied to near the both sides of the low-friction surface of the transport roller, there does not occur a difference in the paper feeding speed at the both end sides of the low-friction surface.
Preferably, the second roller includes a plurality of individual rollers respective widths of which are identical with each other.
In the configuration, the manufacturing cost of the apparatus can be reduced and the management cost also can be reduced due to the decrease of the number of kind of components.
Preferably, the second roller includes a plurality of individual driven rollers. A widthwise dimension of the individual driven roller opposing to the entire width of the first portion of the first roller is larger than another individual driven rollers.
In this configuration, since the action affected on the transport roller by the driven roller opposing to the low-friction surface becomes similar to the action affected on the transport roller by the other driven rollers, the transporting stability of the paper can be further improved.
Preferably, the surface of the second portion of the first roller is defined by a coating layer.
In this configuration, the friction coefficient of the roller capable of obtaining high transporting accuracy can be fabricated easily.
Preferably, a thickness of the coating layer is within a range of 15 xcexcm to 100 xcexcm.
In this configuration, the roller having efficiency suited to the specification of the recording apparatus can be obtained by selecting the thickness of the coating layer.
Preferably, the difference between the first diameter and the second diameter is twice of the thickness of the coating layer.
In this configuration, a difference corresponding to the thickness of the coating film is formed between the low-friction surface and the driven roller. Since the thickness of the coating film is very small, the transporting stability of the paper is prevented from being degraded and the generation of origin of the cockling phenomenon can be suppressed.
Preferably, the second portion of the first roller is arranged in both sides portion of the first portion thereof, and urged by the second roller.
In this configuration, since the paper is restricted in its movement due to the small gap corresponding to the thickness of the coating film between the low-friction surface and the driven roller, the transporting stability of the paper is prevented from being degraded and the generation of origin of the cockling phenomenon can be suppressed surely.